McMillan's Olympic debut came at Tokyo 2020, where he swam the lead-off leg of the 4x200m freestyle relay for Ireland. He set an Irish record in the 200m freestyle with a time of 1:46.66. At the World Championships, he competed for Ireland in 2019 and for Great Britain in 2024. His best finish was fourth in the Men's 4 x 200m Freestyle Relay in Doha, Qatar, in 2024.

Recent Achievements

In July 2024, McMillan participated in the Men's 4 x 200m Freestyle Relay at the Paris La Defense Arena. The event saw teams from various countries, including Australia, Brazil, Canada, China, France, Germany, Greece, Israel, Italy, Japan, Lithuania, South Korea, Switzerland, and the USA. Great Britain secured the top rank with McMillan as part of the team.

Training and Relocation

In March 2022, McMillan moved to Stirling, Scotland, to train at a new centre. This decision came after years of training at Bangor Swimming Club in Northern Ireland. The move aimed to enhance his swimming career by providing better training facilities and opportunities.

Switching Nationalities

McMillan switched his nationality from Ireland to Great Britain to gain a competitive edge. This change required him to sit out a year of international competition before he could compete for Great Britain in 2023. He now trains alongside multi-Olympic medallist Duncan Scott.

Memorable Moments and Inspirations

Qualifying for the Tokyo 2020 Olympic Games remains one of McMillan's most memorable moments. He looks up to Michael Phelps, a swimmer with 28 Olympic medals and 33 world championship medals.

Future Plans

Looking ahead, McMillan aims to continue representing Great Britain in international competitions. His focus remains on improving his performance and achieving new milestones in his swimming career.

Jack McMillan's journey from Belfast to Stirling showcases his dedication and commitment to swimming. With significant achievements already under his belt, he is poised for more success in the future.